1. Field of the Invention
The present invention relates to a control method for a bar feeder for supporting a workpiece in a lathe, and more particularly, to a control method for controlling a bar feeder by force control.
2. Description of the Related Art
Generally, in working an elongated workpiece by means of a lathe, a bar feeder is used to guide the workpiece in the Z-axis direction. One side of the workpiece is supported by means of a bar feeder, while the other side of the workpiece is attached to a Z-axis of the lathe, whereby position control in the Z-axis direction is effected.
Conventionally, this position control of the bar feeder is carried out by means of a controller. During the lathing operation, the position control in the Z-axis direction of the lathe and the position control of the bar feeder must be synchronized with each other. For example, the following method is known as a control method to attain this.
(1) The position control of the Z-axis of the lathe and the position control of the bar feeder in the Z-axis direction are synchronized with each other by controlling the lathe and the bar feeder by means of the same controller.
(2) In the case where the lathe and the bar feeder cannot be controlled by means of the same controller, the bar feeder simply supports the workpiece in a free state without seizing it, and the operation is carried out by the position control of the Z-axis of the lathe only.
However, the aforementioned control method for the bar feeder of the conventional lathe involves the following problems.
(1) When effecting the Z-direction position control of the conventional lathe and bar feeder by means of the same controller, it is necessary to use a controller which serves to control both the lathe and the bar feeder. The controller of this type must be an expensive complicated device. Moreover, the controller of this type must be set corresponding to individual lathes and bar feeders, so that it lacks in general-purpose properties.
(2) When controlling the lathe and the bar feeder individually by means of independent controllers, on the other hand, the two controllers must be synchronized. It is difficult, however, to synchronize the independent controllers.
(3) In the case where the conventional bar feeder is operated in a free state by the control of the Z-axis of the lathe only, a slender workpiece is arched and deflected between the lathe and the bar feeder, so that it cannot be worked with accuracy and stability.